4ks and 64ks share some limitations. Both have to use generated music, both rarely use stored textures. They are both not using precalculated video, even if some groups, starting from Complex, did this in the past.
64ks can use some stored samples, but just one or two may fit the 65536 bytes limit - so using them doesn't give a clear advantage to 64ks anyway.
Finally, the use of shaders everywhere made 64ks and 4ks even more similar than before.

Believe me, I always wanted to do this

Still, 64ks have elements that are not present in 4ks (for now).
For example, Conspiracy's intro from Revision 2016 had some evocative black silhouettes recalling human figures. "Gubernyia" from Macau Exports had some of these too, far in the background. 64ks can have a longer and better "story" inside. Just think of "eidolon" by Poo-brain or of (the unfortunately a bit cheesy) "h-immersion" by Ctrl-Alt-Test. Some 64ks can use gm.dls with a bit of trickery. In general, 64ks can have some additional content inside that makes them more complex and various.

But despite of this, having 60 additional whopping kilobytes often acts like a psychologically inverse mechanism that makes coders waste them.
Take "Off" by Mercury. No matter if they say "we have this new shining engine", "we have the bestest synth in the world", "we have a lot of dust on the camera" ("and hexagonal lens flares too") - their 64k seems a lot more like a 4k (at the point that somebody called it "a screensaver"). The same, unfortunately, goes for the latest intro from Conspiracy.

So, does a modern 4k intro look like an older 64k one?

Let me examine some very good candidates.
For example, "absolute territory" by prismbeings reminded me a lot of old intros like "Fresnel 2" by Kolor or "Transgression 3" by mfx. But if you watch them carefully, you see that "absolute territory" looks more like *one* single scene of Fresnel 2, leaving apart the visual quality of the two productions.

Fresnel 2 vs. Absolute territory

Let's take the one I consider the "state of the art" 4k in 2017, "horizon machine" by Eos and Alcatraz, and compare it to the winner 64k of Revision 2012, "gaia machina". Even if you can visually see the gap in those 5 years (the first "machine" is way better for rendering quality), content-wise, or looking at the camera paths and cuts, or even for the quality of the content and objects in the latter one, "gaia machina" still stands higher than the 2017 4k.
The same thing happens if you compare it to more recent winners of Revision: there is almost no competition there.

It seems clear that a middle placed 64k intro like "Off" or "Vessel" can be compared (and maybe lose) to a top-notch 4k like "horizon machine" or "Joia" by Collapse. But 64k clearly win if we take a better designed, packed and polished intro like "eidolon" or "guberniya".

Guess which one is the 4k and which one the 64k

Now we can ask the final questions.

Has the gap between 4k and 64k reduced?
Maybe. Maybe now 64ks and 4ks have the same shaders, the same synths, the same effects, and they are so close that you can't distinguish a mediocre 64k from a brilliant 4k (but still you can distinguish "Chaos Theory 4k" from "Chaos Theory", I suppose).

Is 4k the new 64k?
Not really. Maybe modern 4ks surpassed the average 64k, but still 4ks are runner-ups compared to a jaw-dropping 64k of 2017 or previous years. And probably they will always be.

P.S.: oh well, I didn't notice but 10 years have passed from this post here.
Seems like I "already" have the task to write the second chapter of 4k history (2007-2017).
Stay tuned for more.